The present invention relates to a modular refrigeration assembly for use in conjunction with a refrigerated structure such as a walk-in cooler or freezer employed in retail and wholesale food outlets. More specifically, the invention relates to an assembly which provides an easily replaced unit for generating a refrigerated air flow for such a structure. The term "refrigerated" in accordance with the present invention is intended to incorporate structures wherein the temperature of the contained air mass is maintained at or in excess of 32.degree. F., such as storage structures utilized for milk and fresh foods and those structures in which the air is maintained below 32.degree. F., for the maintenance of frozen food.
An increased market demand has occurred in the retail food outlet equipment industry for low energy consumption refrigerated storage structures in order to reduce operating costs wherever possible. In the operation of all types of refrigerated structures, it is desirable to include a system for automatically defrosting the evaporator coils. The defrost cycle can be actuated either at set periodic time intervals or when the frost build-up within the coils has reached a certain predetermined condition. The latter type of system is typically thermostatically controlled so as to switch from a refrigeration cycle to a defrost cycle of operation. In this manner of operation, it is possible to avoid any significant frost build-up within the display cabinet such that inoperability and spoilage of food products would occur.
There have been three different approaches for defrosting refrigerated display cabinets in this art. These are, utilizing the electric resistance heaters; passing a compressed refrigerant gas having a high specific heat through the refrigeration coils; and, circulating ambient air through an air conduit in which the refrigeration coils are positioned. Due to the increased cost of energy, more emphasis has been placed on the utilization of ambient air defrost systems as an alternative to the electrical resistant heaters or compressed refrigerant gas defrost systems.
Ambient air defrost systems are more economical to operate due to the fact that the existing specific heat in the ambient air can be employed as the energy source to melt the frost and ice which has accumulated on the evaporator coils. In either the electric resistance heaters or the compressed refrigerant gas systems, additional energy must be expended in order to defrost the coils. The structural components of the air defrost systems must be arranged in such a manner that the warm ambient air is brought into contact with the evaporator coils in a direct and positive manner without incurring large capital costs for the necessary ducts and additional air moving machinery. If an overly complicated air defrost system is employed, the additional capital costs can only be recovered after long operating time periods which have been recently significantly extended due to the rising cost of investment capital.
Another problem in the construction of refrigerated structures for the storage of food products is that the refrigeration systems are sometimes incorporated into the structure in such a way that repair and maintenance is rendered extremely difficult. Another problem with the inaccessibility of the refrigeration machinery is that retail store managers cannot upgrade the energy efficiency of the existing equipment without additional significant retrofitting investments.
The present invention is a solution to the above problems in that a modular refrigeration assembly having an ambient air defrost system incorporated therein is provided for use with walk-in coolers and freezers. The assembly is of a unitary construction which enables the low cost retrofitting of existing refrigeration structures.
U.S. Pat. Nos. 2,923,137 to Swanson; 2,961,845 to Kennedy; 3,698,205 to Perez; 4,023,378 to Kennedy, Butts and Steelman; 4,117,697 to Myers and Kennedy; and 4,124,996 to Kennedy, Butts and Steelman describe refrigerated structures in which a food storage space is incorporated together with a merchandiser display section. By construction, the refrigeration equipment used in conjunction with these structures is contained within them in such a manner that repair and maintenance access is limited. U.S. patent application Ser. No. 6,074 filed Jan. 24, 1979 to Myers, Kennedy, and Perez and assigned to the same assignee as is the present application shows another type of a refrigerated structure. In U.S. Pat. No. 4,117,697 an ambient air band B is utilized as a third air curtain, but ambient air is not employed in order to defrost the refrigeration coils.
U.S. Pat. No. 4,072,488 to Johnston shows a glass door reach-in refrigerated display case in which an evaporator coil is located in the top portion of the case and wherein horizontal trap doors are opened in the top wall of the case in order to provide for an ambient air flow. The refrigeration coils of this case are integral with the entire cabinet structure and are not capable of independent use as a refrigeration assembly for separate structures containing cooled air masses. The refrigeration coil package is not a unit separate from the refrigerated display cases. The horizontal arrangement of the defrost doors also permits the accumulation of dust and debris on and around the horizontally disposed top which then results in contamination of the food storage space. This patent does not provide blocking baffles to protect the mass of the cooled air within the case from contact by the ambient air during the defrost cycle of operation.
Various types of air defrost systems have been employed with respect to refrigerated display cabinets used in retail food outlets. Exemplary of such prior art are: U.S. Pat. Nos. 3,403,525; 3,850,003 and 3,937,033 all to Beckwith et al; 3,082,612 to Beckwith; and 3,226,945 to Spencer.